Armonk Professional CenterA Sovereign Shells Campus
The Armonk Professional Center — brick-and-bronze Class A architecture at 355 Main Street, Armonk, New York.

Armonk, New York — A Sovereign Shells Campus

Armonk Professional Center

A managed campus at 355 & 357 Main Street — 36,007 SF of Class A workplace built as a destination, not a commodity.

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Managed by Sovereign Shells · A North Castle Ventures company

The Campus

Two buildings, operated as one destination workplace

Armonk Professional Center brings 355 and 357 Main Street together as a single, coordinated 36,007 SF campus. Rather than leasing anonymous square footage, tenants join a managed environment where architecture, service, and infrastructure are held to one standard by Sovereign Shells, the campus and property manager. Sovereign Shells is the real estate management arm of parent company North Castle Ventures. Both buildings carry the architectural lineage of Vatche Simonian, expressed through a shared language of brick, glass, stone, and site continuity.

The campus sits on a walkable stretch of Main Street in the hamlet of Armonk, steps from cafés, dining, and everyday services, with major corporate neighbors nearby.

36,007 SF

Two buildings, one campus

355 + 357

Main Street addresses

Class A

Workplace standard

Walkable

Main Street village setting

Corporate neighbors

  • IBM
  • Swiss Re Americas
  • Regeneron
  • Armonk village center

The Buildings

Two addresses, 36,007 SF, one standard

Select a building to explore how 355 and 357 Main work together as a single destination workplace.

355 Main Street — Class A brick-and-bronze architecture with a glazed corner entry.

355 Main is the campus flagship: a fully repositioned Class A building where the ground floor is being released as flexible professional suites, and the second level is home to a full-floor institutional tenant.

Building
14,070 RSF
Class
Class A
Ground floor
2 suites now leasing
Second level
7,590 RSF, leased

Leasing Milestone

The 2nd Level Full-Floor Flagship Suite is leased

Alpha School has signed for the entire second level of 355 Main — the campus's Full-Floor Flagship Suite. It anchors Armonk Professional Center with an institution reimagining K–8 education around adaptive, AI-powered learning.

Learn about Alpha SchoolAbout the owner

Tenant

Alpha School

Suite

2nd Level Full-Floor Flagship

Area

7,590 RSF

Status

Leased

This full-floor commitment is separate from the ground-floor suites at 355 Main, which remain available. See current first-floor availability below.

First-Floor Availability

Ground-floor suites at 355 Main — 2 now leasing

The ground floor of 355 Main is being released as a small collection of turn-key professional suites. Each is delivered to a Class A standard and can be tailored to a tenant's fit-out. Availability reflects current status and is subject to change.

A finished conference room at 355 Main, indicative of the Class A interior standard for ground-floor suites.
Ground-floor suite availability at 355 Main Street
SuiteSizeStatus
Suite 102Shell A1,065 SFNow leasing
Suite 104Shell B1,162 SFNow leasing
Suite 106Shell C1,060 SFOccupied
Inquire about a suite

The Experience

A workplace designed as a destination

The campus is operated to feel like a single, considered place — from the lobby to the sidewalk outside.

Managed, single-owner service

Owned and managed directly by North Castle Ventures — one point of accountability for building operations, maintenance, and tenant experience.

Class A architecture

Limestone, bronze-framed glass, and considered interiors held to a consistent standard across both 355 and 357 Main.

Walkable Main Street setting

Cafés, dining, and everyday services within a short walk in the heart of the Armonk village center.

Turn-key professional suites

Ground-floor suites delivered ready for occupancy, with fit-out tailored to each tenant's needs.

The double-height lobby with a brick feature wall, brass-railed stair, and sculptural pendant lighting.
A landscaped outdoor terrace set against a natural stone retaining wall.
A refined conference room with curved glazing and designer lighting.

Sovereign Shells at Armonk Professional Center

One sovereign campus. Two connected nodes.

Node 1 at 355 Main combines sovereign infrastructure with physical workplace. Node 2 at 357 Main is being implemented for qualified virtual clients. Dark fiber between the sister buildings creates a private campus backbone designed for continuity as needs and space evolve.

Physical workplace

355 Main · Node 1

Sovereign infrastructure with space

Tenant-controlled sovereign AI technology paired with meeting environments, offices, and separately marketed available suites.

Explore Node 1

In implementation

357 Main · Node 2

Sovereign technology for virtual clients

A hosted mini data center designed to extend the same class of sovereign AI technology to up to 75 qualified virtual clients without requiring a dedicated suite.

Review Node 2

Node 2 is in implementation and designed for up to 75 clients; it is not commissioned or currently available for activation. Sovereign Shells manages the campus and property infrastructure. Nate diagnostics and software orchestration are independently operated by Native Agentic.

Discuss your requirements

Location

355 & 357 Main Street, Armonk, New York

In the heart of the Armonk village center in Westchester County — walkable, well-connected, and minutes from major corporate campuses and Westchester County Airport.

Campus address

355 & 357 Main Street

Armonk, NY 10504

  • Armonk village centerWalkable — cafés, dining, services
  • Westchester County Airport~10 minutes by car
  • White Plains~20 minutes by car
  • Manhattan~45 minutes by car
Get directions

Contact

Schedule a campus conversation

Interested in a suite at 355 Main, a private node with physical access, or the future 357 Main presence node? Tell us which pathway fits your requirements.